Hand Tools Archive

Unicorn and Bevel Up

David Weaver
I set up my 18 (I have five total blades for it) thinking it would be easy to find the effect of the unicorn in terms of tearout, only to find at shaving thicknesses that most of us would use, there's not too much tearout except for ribboned and interlocked wood, and then it's never really deep, just a nuisance.

But what I've found out so far is that a 45 degree total bed (25 degree blade, 20 bed on the 18) seems to match tearout performance of a 55 degree blade, but feels closer in push resistance to 45 degrees (and certainly is less faffy to sharpen as using a guide and then dealing with the wire edge on a soft blade is a real pain in the butt).

those "feels" are at equivalent shaving thickness, about 2.5 thousandths.

Bringing me back to where I used to get in trouble before the double iron, especially with japanese planes. It wasn't the thin shavings that were a problem, it was getting nearly done smoothing a surface and then accidentally doing something to advance the iron and then getting huge tearout on a short deep cut. When your only method to control tearout is high angle or thin shavings, that kind of accident is terrifying. It never happens with the double iron - if you set the plane too deep, you can't push it.

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